In the various data processing systems involving transmission of data, such as ADSL, wireless transmission, etc., there is a continuing need to provide error correction for noise that corrupts the data. The noise is often concentrated at a specific point in time so that the data that is corrupted may destroy too much information to be recovered by error correction. Error correction in part relies on having enough good data to be able to make a good estimate as to what the corrupted data actually was. If too much consecutive data is corrupted, there may not be enough good data to form a basis for making the desired error correction. Thus, one of the techniques to avoid a noise spike from creating this problem is to transmit the data in a different sequence and then re-creating the data at the receiving end. One common technique for doing this is called bit interleaving. In such case, alternate bits are transmitted, i.e., all of the even bits are transmitted then all of the odd bits are transmitted. At the receiving end the data is reconstructed by placing the data back in the regular order.
One of things then that is required is the ability to rearrange the data as needed. Typically, this is done with look-up tables or bit by bit mapping. Look-up tables require significant amounts of memory space. The memory space is a precious commodity in a processor such as a DSP for example. There are techniques for reducing the space required of the memory to achieve the look-up capability, but at the disadvantage of reduced speed. The alternative of bit by bit mapping is quite slow and occupies processing capability.
Accordingly, there is a need to be able to rearrange data quickly and with relatively small amount of space.
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